For various applications at the control of combustion engines, in particular at the control of combustion engines for motor vehicles, it is required to determine the vapor pressure of the fuel in the fuel tank. By knowing the vapor pressure of the fuel statements for example can be made about the volatility of the fuel and therefore about the features of the actually used fuel. Traditional procedures usually use a pressure sensor in the fuel tank for determining the vapor pressure of the fuel, whereby the partial pressure of the gaseous fuel vapors can be assumed by measuring the pressure.
But such pressure measurements do not always provide satisfactory results. In particular only the total pressure can be measured. Reliable statements about the partial pressure of the fuel vapors are not possible without further ado. The German patent application DE 102 52 225 A1 suggests therefore for example to determine the vapor pressure of the fuel over the temperature dependency of a parameter of the tank ventilation system, which indirectly correlates with the internal pressure that exists in the fuel tank system. But several mistakes can occur at this indirect determination of the vapor pressure, so that this procedure is also not always satisfactory.
In contrast the invention sets oneself the task to enable a reliable determination of the vapor pressure of the fuel by simple means. Thereby the disadvantages of the state of the art shall be avoided. By the determination of the vapor pressure of the fuel for example statements about the fuel volatility and therefore statements about the features of the actually used fuel shall be made, which can be used for an improvement of for example the transmission compensation, the start enhancement and such alike.